From 80fc24142c0e3e7ed174a8bb82fa42cfa685a448 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marcin=20Wcis=C5=82o?= Date: Tue, 31 Mar 2026 19:17:21 -0400 Subject: [PATCH] KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit jira VULN-180395 cve CVE-2026-23401 commit-author Sean Christopherson commit aad885e774966e97b675dfe928da164214a71605 upstream-diff Used linux-6.1.y backport ed5909992f344a7d3f4024261e9f751d9618a27d for the clean pick. Strictly speaking, the upstream's `kvm_flush_remote_tlbs_gfn(vcpu->kvm, gfn, level)' call corresponds to LTS 9.2-native `kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn & -KVM_PAGES_PER_HPAGE(level), KVM_PAGES_PER_HPAGE(level))'. See the non-backported commits: - 9ffe9265375cbaf6c01647e31ae9fee8595b698c ("KVM: x86/mmu: Fix wrong gfn range of tlb flushing in kvm_set_pte_rmapp()"), - 8c63e8c2176552d5c003d7459609383d32bf47f3 ("KVM: x86/mmu: Rename kvm_flush_remote_tlbs_with_address()"), - c667a3baeddcc982bf512c126aec8d0f04adecfe ("KVM: x86/mmu: Move round_gfn_for_level() helper into mmu_internal.h"). Nevertheless preserved linux-6.1.y's `kvm_flush_remote_tlbs_with_address()' call without `gfn' rounding, as that's exactly how it's used in the same function a few lines later, strongly suggesting that the issues raised in commit 9ffe92653 don't apply here. When installing an emulated MMIO SPTE, do so *after* dropping/zapping the existing SPTE (if it's shadow-present). While commit a54aa15c6bda3 was right about it being impossible to convert a shadow-present SPTE to an MMIO SPTE due to a _guest_ write, it failed to account for writes to guest memory that are outside the scope of KVM. E.g. if host userspace modifies a shadowed gPTE to switch from a memslot to emulted MMIO and then the guest hits a relevant page fault, KVM will install the MMIO SPTE without first zapping the shadow-present SPTE. ------------[ cut here ]------------ is_shadow_present_pte(*sptep) WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292 Modules linked in: kvm_intel kvm irqbypass CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm] Call Trace: mmu_set_spte+0x237/0x440 [kvm] ept_page_fault+0x535/0x7f0 [kvm] kvm_mmu_do_page_fault+0xee/0x1f0 [kvm] kvm_mmu_page_fault+0x8d/0x620 [kvm] vmx_handle_exit+0x18c/0x5a0 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm] kvm_vcpu_ioctl+0x2d5/0x980 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb5/0x730 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x47fa3f ---[ end trace 0000000000000000 ]--- Reported-by: Alexander Bulekov Debugged-by: Alexander Bulekov Suggested-by: Fred Griffoul Fixes: a54aa15c6bda3 ("KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte()") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson (cherry picked from commit ed5909992f344a7d3f4024261e9f751d9618a27d) Signed-off-by: Marcin Wcisło --- arch/x86/kvm/mmu/mmu.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 4e579eacc1208..1f9c7a8f86798 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2792,12 +2792,6 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot, pgprintk("%s: spte %llx write_fault %d gfn %llx\n", __func__, *sptep, write_fault, gfn); - if (unlikely(is_noslot_pfn(pfn))) { - vcpu->stat.pf_mmio_spte_created++; - mark_mmio_spte(vcpu, sptep, gfn, pte_access); - return RET_PF_EMULATE; - } - if (is_shadow_present_pte(*sptep)) { /* * If we overwrite a PTE page pointer with a 2MB PMD, unlink @@ -2819,6 +2813,15 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot, was_rmapped = 1; } + if (unlikely(is_noslot_pfn(pfn))) { + vcpu->stat.pf_mmio_spte_created++; + mark_mmio_spte(vcpu, sptep, gfn, pte_access); + if (flush) + kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn, + KVM_PAGES_PER_HPAGE(level)); + return RET_PF_EMULATE; + } + wrprot = make_spte(vcpu, sp, slot, pte_access, gfn, pfn, *sptep, prefetch, true, host_writable, &spte);